Green sheets must as a rule, in their production, be provided with a number of small holes that are later used for through-contacting conductors that are mounted on the ceramic substrates. These are relatively small holes, of markedly less than one millimeter in diameter, and such holes must be made in large numbers. The punching device has a correspondingly large number of punching dies. The punching dies are provided with heads that are held in a holding device, such as a holder plate, in order to be moved with it in the longitudinal direction of the shaft, or in other words for instance up and down.
A similar punching device is known for instance from European Patent Disclosure EP 0 354 152 B1. The punching dies here are driven by magnet drives. These punching dies are likewise provided with a head that is mounted on the elongated shaft of the punching die.
In performing their job, the punching dies are exposed to a severe abrasive stress. They must therefore be made of a suitable wear-resistant hard material. They are therefore made of an elongated, needle-like body, on which the head, typically of a different material, for engagement by the head plate or other drive mechanisms, is attached later.
As known for instance from U.S. Pat. No. 3,974,728, the working part of a punching die may also be inserted into a body provided with a head and secured to this body for instance by adhesive. However, this makes production relatively complicated. Since punching dies are considered to be wearing parts, it must be attempted to be able to produce them as fast, simply and inexpensively as possible, yet without sacrificing quality. Quality, however, is definitively determined by the straightness or in other words precision of the punching die. Adhesive points between a cylindrical driving body and a cylindrical working part are critical here.
From U.S. Pat. No. 4,700,601, it is also known for punching dies that are intended for punching paper to be provided with a plastic head. To that end, the metal punching die has an annular groove. The region provided with the annular groove is then sheathed with an extruded cylindrical plastic body, whereupon the plastic partly flows into the annular groove and thus makes a positive-engagement connection between the head and the die.
As a rule, the punching dies for green sheets cannot be provided with plastic heads. Because of the small diameter of the shafts of the punching dies, as a rule adequately durable positive-engagement connections are not obtained between a plastic head and the punching die.
With this as the point of departure, it is the object of the invention to create a punching die for a green sheet punching device as well as to create a corresponding punching device; the punching dies should be simple and economical to produce and should meet high standards for quality.